GB1596400A

GB1596400A - Platforms for sea-bottom exploitation

Info

Publication number: GB1596400A
Application number: GB53821/77A
Authority: GB
Original assignee: EMH; Entreprise d'Equipements Mecaniques et Hydrauliques
Current assignee: EMH; Entreprise d'Equipements Mecaniques et Hydrauliques
Priority date: 1977-06-24
Filing date: 1977-12-23
Publication date: 1981-08-26
Also published as: NL7714334A; JPS5410502A; JPS5626727B2; CA1066523A; DE2758339A1; NO148819B; SU1064874A3; BR7708670A; NO148819C; FR2395359A2; ES465480A1; AR217097A1; FR2395359B2; SU882421A3; NO774476L

Description

(54) IMPROVEMENTS IN OR RELATING TO PLATFORMS FOR SEA-BOTTOM EXPLOITATION (71) We, ENTREPRISE DrEQUlPEMENTS MECANIQUES ET HYDRAULIQUES EMM, a French body corporate of 29 rue de l'Abreuvoir - 92100 Boulogne Billancourt, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a sea-bottom exploitation or development platform comprising mooring and loading column provided with a base intended to be sunk to the sea bottom on the selected erection site.

There is described in the patent application No. 27022/77 (Serial no 1581371) a type of column articulated to base, intended to be erected on the sea bed by sinking the base to the bottom by filling ballast tanks incorporated in the structure of the base. However, an articulated column described in that patent application may not be used with advantage unless it is installed on development sites at relatively great depth of the order of one hundred meters or more. Indeed, such an articulated column must be provided with floats allowing it to be maintained in substantially vertical relationship to its base lying on the sea bed. At smaller depths the sizes of the floats must be increased to ensure a sufficient righting moment on the column.This increased size of the floats, however, renders the column much more heavesensitive, so that in medium depths of the order of from 40 to 60m, the articulated column becomes much less advantageous.

On the other hand, the known system using mooring buoys anchored by means of chains suffers from many drawbacks, including rapid wear of the chains and of the flexible oilloading pipes. The column for sea-bottom exploitation according to the present application is remarkable in that it requires no mooring chains for its installation, in that the oil-supply pipes connected thereto are subjected to no strain or wear (they may be rigid) and in that it requires no righting floats, as an articulated column does, since it is rigidly secured to its base.

The installation of the present application therefore represents an improvement in or modification to the invention of the abovementioned earlier application, in that the column is at all times rigidly secured perpendicularly to the base, and can therefore provide an excellent solution for medium-depth exploitation or development sites.

In one aspect the present invention provides a sea-bottom exploitation or development platform comprising a column rigidly attached to a base so as to extend perpendicularly therefrom, the base having a plurality of straight sides and comprising a plurality of ballast tanks, which provide buoyancy when the platform is floating, the tanks being selectively ballastable so that the floating base can be tilted in one direction until one of said straight sides engages the sea bed with an opposite side still floating and then tilted in the opposite direction until the base rests on the sea bed.

In another aspect the present invention provides a method for installing a sea-bottom exploitation or development installation which comprises a ballastable base having a plurality of straight sides and a column attached to the base; which method comprises tilting the floating base by unsymmetrical ballasting until one side of the base contacts the sea bed while an opposite side remains at sea level, then further ballasting the base to tilt it in the opposite direction until it rests on the sea bed, the column being throughout the entire process rigidly secured to the base so as to extend perpendicularly therefrom.

In a third aspect the present invention provides a sea bottom exploitation or development installation comprising a platform as described above with its base resting on the sea bed and its column projecting vertically upwardly therefrom and emerging from the sea the depth of which is less than the dimension between said one straight side and said opposite side of the base.

The base preferably comprises a substantially frame-shaped structure with straight sides, at least a portion of the frame being provided with ballasting tanks, the column being mounted in perpendicular relationship to the plane of the base and substantially at its centre, and connected to the said frame through connecting elements extending in substantially transverse relationship to the longitudinal axis of the column.

The aforesaid connecting elements may also be designed as ballasting tanks (the ballasting mass may consist of concrete, iron scrap, lead shots, baryta or any other material whose density is sufficient to reliably fix the base on the sea bed by gravity).

On the other hand, the fact that the said transverse diemnsion of the frame is greater than the depth of the sea bottom allows the submersion of the base to be performed by a particularly accurate and reliable method.

The progressive filling of the ballasting tanks of the base allows a controlled sinking motion of the latter and its accurate positioning on the sea bed.

The invention of this application will be better understood and other possible purposes, details and advantages of the latter will appear more clearly from the following description with reference to the appended non-limitative drawings wherein: Figure 1 is an elevational view of a mooring and loading column, with a portion broken away upon the section line I-I of Figure 2; Figure 2 is a top view, to a smaller scale, of the base upon the section line Il-Il of Figure 1; Figure 3 is a sectional view upon the line III-III of Figure 1, to a larger scale; and Figures 4 to 10, as well as Figures 5a, 6a, 8a and 9a, are diagrammatic views of the same column and its base, illustrating a preferred method of erecting the same on the selected exploitation site.

Referring more particularly to Figures 1 to 3, there is shown a sea-bottom exploitation or development platform 11 which in this case consists more particularly of a mooring and oil loading column 12 rigidly secured to a base 13 intended to be sunk to the sea bed. The upper portion of the column 12 is equipped with a pivoting mooring system 14 (such as the one described for example in British patent no.

1 449 103 or patent application no 45549/76 (Serial No. 1555346)) and may be provided with a helicopter-landing upper-deck or helipad 15 and more generally with all equipment necessary for its operation, motors and pumps.

The base is made up substantially of a frame 16, which is square in the example described and is provided with ballast chambers or tanks and of a column 12 mounted at the center of the said frame in perpendicular relationship to its medial plan, the said column being connected to the frame through connecting elements 17 extending in substantially transverse relationship to the longitudinal axis of column 12. The connecting elements 17 are themselves adapted to serve as ballast chambers or tanks. Moreover, it is important to note tht the length of one of the sides of the square frame 16 (or at least one transverse dimension of the frame if it has a different shape) is greater than the depth of the sea bed on the installation site.This feature combined with the method of submersion of the platform which will be described later, allows the base to be accurately and reliably positioned on the selected erection site. The said transverse dimension is at least 40% and preferably at least 50So, greater than the said sea-bed depth and may notably constitute the longitudinal dimension of the base in the particular case where the latter is substantially rectangular.

In the example described the connecting elements 17 form a cross-brace, the arms of which extend along the mid-perpendiculars of the frame 16. The said arms, however, may alternatively extend along the diagonals of the frame. Each connecting element 17 is of rectangular-section tubular structure (Figure 3) defining a ballast chamber or tank R1 , R2, R3, R4 adapted to receive ballast 17a, e.g. of concrete. Furthermore, also each side A, B, C or D of the frame 16 is of tubular structure (of circular section in the example illustrated) and is transversely partitioned (walls 20) into several sections defining the above-mentioned ballast chambers. Si, according to the form of embodi ment represented in Figures 1 and 2, three such chambers are provided along each side.The side A has three chambers or tanks RAI, RA2, RA3 the side B is made up of the chambers or tanks Rub,, RB2 and RB3 , the side C consists of the chambers or tanks RC1 , RC2 and RC3 and the side D comprises the chambers or tanks RDI, RD2 and RD3.

The base 13 is also provided with stabilizing float-tanks 22 connected to the frame 16. These tanks may be for example four in number and so arranged as to form a square as can be seen in Figure 2 where the tanks 22 are illustrated in phantom lines, so that each tank is located at the middle of one of the sides of the frame 16.

On the other hand, the sides A, B, C and D of the frame 16 are longitudinally provided with stiffening elements 25 projecting under the frame so as to be embedded in the sea floor when the base is installed, thus resulting in improved stability. The same applies to the connecting elements 17, which are also provided with longitudinal stiffening means such as 26.

Lastly, it should be noted that anti-scouring panels 27 are hingedly mounted along the sides A, B, C and D. They are held upward before and during the installation of the platform and then folded down against the sea bed (situation pre represented in Figures 1 and 2) so as to prevent the ground around the base from being scoured under the action of the moving water; The method of installing the platform on the selected site will now be described with reference to Figures 4 to 10.

The platform 11 is first floated. For that, it is sufficient that the above-described ballast tanks should be substantially empty. The platform (Figure 4) is then towed to the selected installation site. Thereafter, the ballast tanks R1, R2, R3 and R4 provided in the elements 17 connecting the column 12 to the frame 16 are simultaneously filled. This stage of the pro cess illustrated in Figures 5 and 5a is continued untill practically the whole base is submerged in proximity to the water surface. At this stage, the tanks 22, being empty, stabilize the platform. It is then sufficient to progressively fill some of the tanks of the frame 16 to cause it to tilt (Figure 6) about one of its sides remaining substantially at the surface of the water.

Thus, as shown in Figures 6 and 6a, if it is desired to cause the base to tilt about its side C, it is sufficient to progressively fill the ballast tanks RB2 and RD2 of the lateral sides B and D and also the stabilizing tank 22 of the opposite side A (or the tank RA1) until the said opposite site A engages the sea bed. This situation is illustrated in Figure 7. It should be noted that, at this stage, the base is at an angle of about 450 to the sea bed, leaving the upper portion of the column emerged, and at one of the sides of the said base has already engaged the sea bed whereas the other side is still emerged. This ensures considerable safety and high accuracy in installing the platform.For example, if it were found that, at this stage of the submersion of the base, the latter is not correctly positioned it would be sufficient to reintroduce air into the lateral tanks RB2 , RD2 or into the stabilizing tank 22 to cause the side A of the base to rise slightly, to change the position of the latter and to again cause the base to tilt until the side A again engages the sea bed. Then the frame 16 is again caused to pivot in the other direction, but this time about the line along which the side A bears upon the sea bed, preferably by first filling the tanks RBI and RD1 of the lateral sides B and D (Figures 8 and 8a), and then the tank RCI of the side C (Figures 9 and 9a) until the whole frame 16 finally lies on the sea bed at the desired location.Thereafter the filling of all the other tanks of the frame 16 is completed and the antiscouring panels 27 (Figure 10) are folded down to stabilize the platform.

It should be noted that the equilibrium of the platform is ensured during the double tilting of the base, the angular position of the latter being constantly controlled by progressively filling the tanks. Of course the described filling sequence of the ballast and/or stabilizing tanks in installing the platform on the exploitation site is given only by way of example and many modifications in the described process of installation of the platform may be contemplated without however departing from the scope of the present invention.

WHAT WE CLAIM IS: 1. A sea-bottom exploitation or development platform comprising a column rigidly attached to a base so as to extend perpendicularly therefrom, the base having a plurality of straight sides and comprising a plurality of ballast tanks which provide buoyancy when the platform is floating, the tanks being selectively ballastable so that the floating base can be tilted in one direction until one of said straight sides engages the sea bed with an opposite side still floating and then tilted in the opposite direction until the base rests on the sea bed.

2. A method for installing a sea-bottom exploitation or development installation which comprises a ballastable base having a plurality of straight sides and a column attached to the base; which method comprises tilting the floating base by unsymmetrical ballasting until one side of the base contacts the sea bed while an opposite side remains at sea level, then further ballasting the base to tilt it in the opposite direction until it rests on the sea bed, the column being throughout the entire process rigidly secured to the base so as to extend perpendicularly therefrom.

3. A sea-bottom exploitation or development installation comprising a platform of claim 1 with its base resting on the sea bed and its column projecting vertically upwardly therefrom and emerging from the sea the depth of which is less than the dimension between said one stright side and said opposite side of the base.

4. A platform according to Claim 1 wherein the base is substantially symmetrical with respect to a vertical central axis thereof, and has a structure substantially in the form of a frame whose periphery is defined by a plurality of straight tubular side members provided with ballast tanks or chambers, the tanks of at least one side member being fillable independently fromthose of the other side members, the column being mounted in perpendicular relationship to the plane of the frame and substantially at its centre and connected to the frame by connecting elements extending in substantially transverse relationship to the longitudinal axis of the column and forming a cross-brace construction within the frame.

5. A platform according to claim 4, wherein at least part of the said connecting elements are designed as ballast tanks or chambers.

6. A platform according to claim 4 or claim 5 wherein the frame is substantially square and the connecting elements form a cross-brace the arms of which extend between the mid-points of opposite side members or along the diagonals of the said frame.

7. A platform according to any one of claims 4, 5 and 6, wherein stabilizing float tanks are connected to the said frame.

8. A platform according to claim 7, wherein the stabilizing tanks are four in number and arranged symmetrically with respect to the central axis of the base, in such a manner that each stabilizing tank is connected to the middle of one of the sides of the frame.

9. A platform according to any one of claims 4 to 8, wherein the sides of the frame are of tubular structure and transversely partitioned into several sections defining the said ballast tanks.

10. A platform according to any one of claims 4 to 9, wherein the sides of the frame

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cess illustrated in Figures 5 and 5a is continued untill practically the whole base is submerged in proximity to the water surface. At this stage, the tanks 22, being empty, stabilize the platform. It is then sufficient to progressively fill some of the tanks of the frame 16 to cause it to tilt (Figure 6) about one of its sides remaining substantially at the surface of the water. Thus, as shown in Figures 6 and 6a, if it is desired to cause the base to tilt about its side C, it is sufficient to progressively fill the ballast tanks RB2 and RD2 of the lateral sides B and D and also the stabilizing tank 22 of the opposite side A (or the tank RA1) until the said opposite site A engages the sea bed. This situation is illustrated in Figure 7. It should be noted that, at this stage, the base is at an angle of about 450 to the sea bed, leaving the upper portion of the column emerged, and at one of the sides of the said base has already engaged the sea bed whereas the other side is still emerged. This ensures considerable safety and high accuracy in installing the platform.For example, if it were found that, at this stage of the submersion of the base, the latter is not correctly positioned it would be sufficient to reintroduce air into the lateral tanks RB2 , RD2 or into the stabilizing tank 22 to cause the side A of the base to rise slightly, to change the position of the latter and to again cause the base to tilt until the side A again engages the sea bed. Then the frame 16 is again caused to pivot in the other direction, but this time about the line along which the side A bears upon the sea bed, preferably by first filling the tanks RBI and RD1 of the lateral sides B and D (Figures 8 and 8a), and then the tank RCI of the side C (Figures 9 and 9a) until the whole frame 16 finally lies on the sea bed at the desired location.Thereafter the filling of all the other tanks of the frame 16 is completed and the antiscouring panels 27 (Figure 10) are folded down to stabilize the platform. It should be noted that the equilibrium of the platform is ensured during the double tilting of the base, the angular position of the latter being constantly controlled by progressively filling the tanks. Of course the described filling sequence of the ballast and/or stabilizing tanks in installing the platform on the exploitation site is given only by way of example and many modifications in the described process of installation of the platform may be contemplated without however departing from the scope of the present invention. WHAT WE CLAIM IS:

1. A sea-bottom exploitation or development platform comprising a column rigidly attached to a base so as to extend perpendicularly therefrom, the base having a plurality of straight sides and comprising a plurality of ballast tanks which provide buoyancy when the platform is floating, the tanks being selectively ballastable so that the floating base can be tilted in one direction until one of said straight sides engages the sea bed with an opposite side still floating and then tilted in the opposite direction until the base rests on the sea bed.

and/or the connecting elements are provided longitudinally with stiffening elements preferably projecting underneath the said frame.

11. A platform according to any one of claims 4 to 10, wherein anti-scouring panels are hingedly mounted along the sides of the said frame so as to be raisable and lowerable against the sea bed.

12. A method according to claim 2 wherein the base is substantially symmetrical with respect to a vertical central axis thereof, and has a structure substantially in the form of a frame whose periphery is defined by a plurality of straight side members, said frame comprising ballast tanks or chambers, the column being mounted in perpendicular relationship to the plane of the frame and substantially at its centre, and connected to the frame by connecting elements extending in substantially transverse relationship to the longitudinal axis of the column; at least one transverse dimension of the said frame being greater than the depth of the sea bottom at the selected installation site; the method comprising the steps of: floating the said installation to the selected installation site, said ballast tanks being substantially empty, Symmetrically ballasting the base until substantially the whole base is submerged in proximity to the surface of the water, causing the said frame to tilt about one of its sides remaining substantially at the surface of the water, by progressively ballasting some of the tanks on an opposite side and/or lateral sides until said opposite side engages and rests on the sea bed, and causing the frame to pivot in the other direction about the line along which the said opposite side bears upon the sea bottom, by progressively ballasting the tanks on said one side and/or the said lateral sides, until the whole of the said frame rests on the sea bed.

13. A method according to claim 12, wherein said transverse dimension is at least 40% greater than the sea-bottom depth.

14. A method according to claim 12 or claim 13, wherein substantilly all the tanks of the said frame are thereafter filled to ensure the final stability of the platform.

15. A method according to any one of claims 12 to 14, for installing a platform according to claim 11, wherein the antiscouring panels are folded down after the said frame is laid on the sea bed.

16. A platform substantially as described herein with reference to and as shown in the accompanying drawings.

17. A method substantially as described herein with reference to and as shown in the accompanying drawings.